Mold wash



Patented Apr. 1, 1930 I I UNITED STATES mm: L. BRADEN, or YOUNGSTOWN,01110 MOLD WASH N Drawing.

In casting molten metal it has long been the practice to coat the moldprior'to casting with various compounds for the purpose of protectingthe mold, improving the surface ofthe casting and facilitating the sep-'aration of the casting from the mold after the casting has becomesufficiently solid to permit its removal therefrom. These compounds areordinarily referred to as mold washes and the present invention relatesthereto.

Little is known about the exact reaction occurring at the point ofcontact of themolten metal, and the coating of mold wash during thecasting operation. It is thought by some that the carbonaceous washesburning away ahead of the metal produce a reducing atmosphere therebyreducting the oxidation on the surface of the metal and thus tending tomake it more fluid, while others think that the wash partly distills orburns away as just described but that it leaves a coating of graphite orcoke which enters the metal, producing a slight increase in carbon,which,

however, is probably only temporary, at the surface of the metal andthereby renders it more fluid. In any case it is believed that thefluidity of the metal around the mold and adjacent its point of contacttherewith is an important factor in producing a smooth,

sound casting.

It is common steel mill practice to teem molten steel into metal moldsin the production of steel ingots, the molds being filled with moltenmetal while their temperature is at any point between atmospheric orroom temperature and 400 centrigrade or even higher. When a mold wash isemployed, the molds are coated therewith prior to the teeming operationand while Within a similar temperature range, the length of time betweenthe application of the wash and the teeming of the metal being anythingfrom a few minutes to two hours or more. Upon'the application of thewash to themold acertam amount of the more volatile constituents of thewash are distilled off in accordance with the temperatureof the moldthereby leaving the heavier, relatively less volatile constituents toform the residual coating on the mold,

Application filed August 3, 1927. SerialNo. 210,465.

and I have found that the amount of the residual coating has a materialeffect on the behavior of the steel or other metal when teemed into themold, castings having defective surfaces being produced if either toomuch or too little of this residual coating is present.\ The defects inthe surfaces of the castings due to these conditions cannot well beremoved in subsequent operations upon the ingot.

I have found it possible, in accordance with the present invention, tocompound a mold wash of such ingredients and in such manner that whenapplied to a mold when the latter is at a predetermined temperature, thequantity or amount of residual coating which is ultimately left ordeposited on the mold may be controlled within practical limits, inconsequence of which it ,is possible to form on the surface of the molda residual coat-' ing having suitable characteristics to produce a highquality of casting having smooth, sound surfaces.

As the principal ingredient or base for my improved mold wash, I utilizea'suitable hydrocarbon having a high decomposition temperature and forthis purpose prefer to employ crude tar either alone or mixed withdehydratedtar, partially distilled tar,,pitch or other resinousmaterials. Natural or artificial asphalts or petroleum still residues aswell as fatty oils and waxes of vegetable origin may also be employed asbases for thewasln However, I have found that good results may beobtainedfrom the use of crude tar, and as this material is relativelycheap and readily procurable I prefer to utilize it under mostconditions.

This hydrocarbon base is mixed in any convenient manner with a suitablesolvent or thinner and for this purpose I prefer to employ creosote oilalthough if desired other like oils or tar oil fractions, rosin oil,paint thinners or petroleum oils of proper volatility and solvent actionmay. be employed. However, as in the case of the crude tar, creosote oilis a readily obtainable and relatively cheap material and I thereforeprefer to employ it as the solvent under most conditions.

When the mold wash is to be heated before being applied to the mold theaddition of any other ingredients beside the base and the solvent isunnecessary the heating rendering the wash sufiiciently uid forconvenient ap: plication but when the wash is to be applied cold, thatis, substantially at room temperature, I prefer, with a view torendering the wash sufliciently fluid for convenient application, to adda suitable quantity of'naphthalene which material as is well known,progressively increases the fluidity of tar when added thereto in aquantity up to about 20% of the total weight of the mixture, maximumfluidity being attained at this point.

As the several ingredients of the wash all contain more or less volatileingredients or fractions which distill off in the presence of heat, Itherefore, in preparing my mold wash, so calculate the proportions ofthe ingredients as to bring about the deposit of a predeterminedresidual coating on the mold surface when the wash is applied to themold when the latter is at a given temperature. Thus, if the wash is tobe applied to the molds at atmospheric or room temperature, under whichconditions there will be a relatively small loss of the volatileconstituents by distillation from the heat of the mold, I so determinethe proportions of the ingredients in the wash that the ultimate coatingon the mold will conform to the desired condition while, on the otherhand, if the wash is to be applied to the mold when the latter is veryhot as, for example, 400 centigrade or even higher, I ma so proportionthe ingredients of the was that the ultimate residual coating after therelatively great distillation and volatilization of ingredients of thewash efi'ected by the heat of the mold has taken place will conform tosubstantially like conditions.

Thus, with this end in view, in com ounding the wash I take anyconvenient mo (1 temperature as a guide, for exam le, 400 centigrade,and then distill at thls temperature,

referabl se aratel sam les of the several P y p p I S added as well asto the naphthalene frac- Ingredients of which the wash is to be composedand which embody fractions volatilizable at or below that temperatureand note the residual percentagesmf the tin edients after suchdistillation is effected. mm the data thus obtained the relativequantities of the different ingredients to be included in the mold washmay be readily calculated so as to produces. wash from which, when it isapplied to the mold at a temperature substantially corresponding to thatat which the distillation of the samples was efiected, a definitepercentage or fraction of the whole quantity employed will bevolatilized by the heat of the mold, thus leaving the desired amount ofresidual coating thereon.

As an example of one manner of compounding my mold wash from tar andcmsote oil in accordance with the present invention, it may be assumedthat the wash is to be applied to the molds when thelatter are at atemperature of approximately 400 centigrade and that it is desired toleave on the mold a residual coating of substantially 37% of the totalamount of wash employed, this percentage having been found in practlceto give very satisfactory results. Under these conditions samples ofboth the tar and the creosote oil may be distilled separately at 400centigrade and the percentages of residuum of each sample at thetermination of the distilling operation duly noted. From thesepercentages the quantity of each ingredient which must be used toproduce the desired residual percentage of 37% may be readily calculatedand the mold wash then compounded from the ingredients in correspondingproportions which, in the present example, will approximate 75% byvolume of tar and 25% y volume of creosote oil.

It will of course be understood that if a greater or lesser amount ofresidual coating is desired on the mold when the latter is to be coatedat the assumed temperature of 400 centigrade, the proportions of theingredients will be correspondingly varied and, equally, that if themolds are to be coated at some other temperature, either higher orlower, than 400 Centigrade the distillation of the samples of theingredients will be efl'ected at such temperature and the properproportions of the ingredients which are to be compounded to formthewash determined from the percentage of residuums of the severalingredients as ascertained by such test distillation.

When the mold wash is intended to be a plied to the molds withoutpreheating tl ie wash, the addition of naphthalene is desirable torender the wash sufficiently fluid for convenient application; fluiditybeing particularly advantageous when the wash is to be applied to themolds by spraying. Under these conditions consideration must also beiven to the efiect of the naphthalene which tions of the tar or otherbase and of the cresote oil or other thinner or solvent in determiningthe proper proportions of the ingredients of the ultimate mixture whencalculatin the same from the residuums left after dlstillation of thetest samples.

Powdered graphite may sometimes be added to the wash with beneficialresults in quantities running up to approximately 20% of the totalvolume of the latter while, if desired, addition may also be made offire extinguishing chemicals such as carbontetrachloride for the purposeof reducing the fire hazard.

The wash prepared as hereinbefore described may be ap lied to the moldsin any convenient way as by means of a brush or by a suitable sprayingapparatusand either considerably in advance of the time when the metalis to be teemed into the molds or only a short time in advance thereof,the coating being preferably made as uniform as possible and ofsubstantially even thickness in accordance with the usual practice.

While my improved mold wash is especially suited for use upon metallicmolds in which steel is to be cast, it may be used with bene- I ficialresults on other forms of molds designed for the reception of moltensteel or on metallic or other molds in the casting of metals other thansteel such, for example,

1. A mold wash intended for application to the surfaces of molds inwhich metal is to be cast, comprising a hydrocarbon base having a highdecomposition temperature and creosote oil.

2. A mold wash intended for application to the surfaces of molds inwhich metal is to be cast, comprising tar and creosote oil.

- 3. A mold wash intended for application to the surfaces of molds inwhich metal is to I be cast, comprising a hydrocarbon base having a highdecomposition temperature, creosote oil and naphthalene.

4. A mold wash intended for application to the surfaces of molds inwhich metal is to be cast, comprising tar, creosote oil and naphthalene.

5. A mold wash intended for application to the surfaces of molds inwhich metal is to be cast, comprising substantially 75% by .volume oftar and 25% by volume of creosote oil.

In wltness whereof, I have hereunto set my hand this 22nd day of July,1927.

HARRY L. BRADEN.

